Night vision systems are used in a wide variety of military, industrial and residential applications to enable sight in a dark environment. For example, night vision systems are utilized by military aviators during nighttime flights or military soldiers patrolling the ground. As another example, security cameras use night vision systems to monitor dark areas.
Conventional image intensified night vision equipment utilize an image intensifier (I2) to amplify a low light level (LL) scene. The image intensifier collects tiny amounts of light in a dark environment, including the lower portion of the infrared light spectrum, that are present in the environment but may be imperceptible to the human eye. The image intensifier amplifies the light so that the human eye can perceive the image. The light output from the image intensifier can either be supplied to a camera or directly to the eyes of the viewer. Image intensifier devices are commonly used in night vision goggles, i.e., a monocular or binocular, that are worn on a user's head for transmission of light output directly to the viewer.
Night vision systems typically do not include an autofocus device. Conventional autofocus devices include an objective lens, an electronic imaging device (such as a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) circuit), an electro-mechanical driver for positioning the objective lens relative to the imaging device and an electronic processor that performs real-time image analysis. In operation, the electronic processor determines a suitable focus adjustment based on the real-time image analysis. The electronic processor sends focus commands to the electro-mechanical driver to position the objective lens for optimal focusing of the image.
Because the processor is continually analyzing the image, and may adjust the objective lens over a wide range of focus positions, continuous electrical power is generally used by the autofocus components. In a conventional application, the power provided to the autofocus components may represent a significant percentage of the available power. For applications that are carried by an individual and are battery operated, the total operating time from a single battery charge may be strongly influenced by the power consumption by the autofocus device. In addition, the weight of existing autofocus devices, in particular, the weight of the electro-mechanical driver and battery components, tends to reduce the mobility of the observer.